1. Field of the Invention
The present invention relates to navigation and, in particular, to a visual, audible, or tactile directional indicator for navigation, and especially for underwater navigation.
2. Description of the Background
Safe and accurate underwater navigation requires the use of a compass, and there are many commercially available varieties suited for underwater use. Conventional underwater compasses are analog indicators which attach to the wrist. However, reading of the wrist-mounted compasses is difficult. The diver cannot focus his/her eyes on the indices of the compass while his/her head and hands are moving in the water. Hence, the diver must be repositioned to allow for an accurate reading, and the wrist must be situated such that the compass indicia are in focus. The diver's attention must be directed entirely to the compass during the reading. Consequently, he/she may overlook surrounding dangers or may stray from the immediate path and collide with underwater rocks, etc. Many other problems arise. For instance, any analog compass will require the diver to memorize critical directions such as the heading back to shore. Such numbers are easily confused or forgotten, and the results can be catastrophic. Moreover, the compass becomes useless without ambient or supplemental lighting.
There have been efforts to improve upon the wrist mounted compasses. For instance, mask compasses are shown and described in U.S. Pat. No. 4,953,304 issued to Raitmaa and U.S. Pat. No. 3,210,859 issued to Fisk. In both designs, a compass is mounted on a support assembly which is pivotally attached to the diving mask. The compass can be pivoted from a stored position on top of the mask to a viewing position at the face of the mask. This maintains a predetermined optical path length, hence there is no need to refocus the compass at each use. However, the advantages stop there. Both patented designs require an optical lens to permit the eye of the diver to focus upon the intricate markings, and the proper numerical headings must still be memorized. Moreover, the compasses substantially block the diver's vision from one eye. This is undesirable because an accurate depth perception is required to prevent underwater collisions. Further problems often arise. For instance, if the mask becomes dirty or foggy, the compass may be obscured, and the diver can no longer use the navigational device. If salt water enters the diver's eyes, focussing may become impossible. After prolonged use, the diver suffers from eye fatigue since one eye is directed to the compass. Manufacturing problems also arise. For example, the requisite lenses are expensive, and the devices must be calibrated for a variety of masks and face shapes to insure the proper focus.
The prior art also includes electronic devices which create a compass using a magnetic sensor coil of wire and an electronic circuit rather than a rotating magnet. These are known as "Fluxvalve" or "Earth inductor" designs, and signals generated by the circuit are capable of activating digital or analog displays. An example of the "Earth inductor" is described in U.S. Pat. No. 4,139,951 issued to Cunard, said patent herein being incorporated by reference.